氮沉降与种间共进化历史对粗毛牛膝菊和本地种竞争格局的影响

Elevated nitrogen deposition significantly affects the invasion processes of alien plants. Most previous studies upon the responses of invasive plants to elevated nitrogen deposition have relied on the comparisons of plant traits, but have unconsciously neglected the potential effects of native plants, especially those sharing coevolutionary history with the invaders. Moreover, intra-specific differentiations commonly occur among invasive core (the initially established populations in invasive range) and marginal populations (the recently established populations during range expansion) of a given invasive plant species. However, the underlying effects of such differentiations on the spreading of invasive plants are not discussed in most of these studies. All these aspects would lead to inaccurate predictions on the expansion of invasive plants with the ongoing elevation of nitrogen deposition. We hypothesize that, under elevated nitrogen deposition, the response and inter-specific competition of invasive and native plants would be shaped by their coevolutionary history, and that compared to old competitors (sharing a longer coevolutionary history with the invader), new competitors (sharing a shorter coevolutionary history with the invader) would more strongly inhibit the alien’s invasion in the future. To test this hypothesis, we plan to conduct a series of experiments (including field survey and greenhouse experiments) to compare the differentiations on growth, reproduction, spreading and genetic traits of the marginal and core populations of the invasive herb Galinsoga quadriradiata. The methodology of “space-for-time substitution” would be employed for the experimental design. The native competitors accompanying marginal invasive populations would be used as new competitors, and those accompanying the core populations as old competitors. Firstly, the genetic and spreading traits differences between marginal and core populations of G. quadriradiata would be explored by field survey. Then, the responses of the two types of invasive populations to simulated nitrogen deposition (CK, 0 g N/m2/yr; Low, 3 g N/m2/yr; Middle, 6 g N/m2/yr; High, 12 g N/m2/yr) would be compared by a greenhouse experiment with complete randomized design. Finally, old native competitors, new native competitors, and prospective competitors (sharing no coevolutionary history with the invader) would be included in an inter-specific competition experiment with the same nitrogen treatments as above-mentioned to simulate different competitive conditions that invaders have undergone during its rang expansion. By this project, we attempt to reveal the synergetic effects of coevolutionary history, inter-specific differentiation and nitrogen deposition on the expansion of G. quadriradiata in the future. Our project represents an initial exploration on the relationship between plants coevolutionary history and invasion process, and would significantly enrich our knowledge about the mechanisms of inter-specific competition and invasive-native plants coevolution. Our findings would also be useful for predicting the potential expansion range of G. quadriradiata under the conditions of elevated nitrogen deposition in the future, and eventually facilitate control, management and prevention of its invasion.

氮沉降的增加显著影响了外来植物的入侵进程，当前的研究多是基于个体水平的物种特性的研究，忽略了本地种与入侵种之间的共进化历史（新、旧竞争者）和入侵种种群间的分化对入侵进程的潜在影响。这些将造成难以准确预测入侵种未来的入侵动态。我们假设：入侵种与本地种在氮沉降增加下的竞争结果将取决于两者之间共进化历史的长短，即新竞争者将更强烈地抑制入侵。本项目拟采用“以空间代时间”的方法，以粗毛牛膝菊扩散边缘种群（与本地种共进化历史短）与中心种群（与本地种共进化历史长）为研究对象，对比两种群间遗传、繁殖与扩散特性差异，及对氮沉降增加的响应差异，并深入探究扩散过程中的新、旧和未来竞争者（无共进化历史）对其生长与扩散的不同影响，揭示其与本地种的种间相互作用和扩散机制。该研究是对物种共进化、种间相互作用机制研究的创新与深化发展，将为准确预测氮沉降增加背景下粗毛牛膝菊的入侵动态和科学防治该种入侵提供坚实的理论依据。

氮沉降的增加显著影响了外来植物的入侵进程，当前的研究多是基于个体水平的物种特性的研究，忽略了本地种与入侵种之间的共进化历史（新、旧竞争者）和入侵种种群间的分化对入侵进程的潜在影响。我们提出假设：入侵种与本地种在氮沉降增加下的竞争结果将取决于两者之间共进化历史的长短，即新竞争者将更强烈地抑制入侵。本项目采用了“以空间代时间”的方法，通过野外调查和同质园控制实验，对比分析了粗毛牛膝菊（Galinsoga quadriradiata）扩散边缘种群（与本地种共进化历史短）与中心种群（与本地种共进化历史长）之间在种子形态、传播力、遗传、竞争力等方面的分化，及其对氮沉降的响应。研究结果表明： .（1）粗毛牛膝菊中心种群的遗传多样性指数高于边缘种群，但遗传分化系数（Gst）低于边缘种群。地理距离和遗传距离间存在显著的正相关关系，暗示了地理因素对粗毛牛膝菊种群遗传结构的形成有影响。.（2）粗毛牛膝菊中心种群的种子扩散力显著高于边缘种群，种群的遗传多样性与种子扩散力之间显著正相关。.（3）粗毛牛膝菊的中心种群对氮沉降的响应水平更高，在个体水平上能获得更高的生长优势。同时，中心种群在竞争中受到的种间相互作用低，容易获得竞争优势。这说明了，中心种群比边缘种群拥有更强的竞争力，在同等条件下，中心种群具有更高的扩散潜力。.（4）粗毛牛膝菊种群之间对氮沉降的响应存在显著差异，中心种群具有更高的响应，然而由于氮沉降的增加同时也促进了本地竞争者的生长，因此，氮沉降的增加导致粗毛牛膝菊受到了更高的竞争抑制作用；与粗毛牛膝菊之间拥有更长的共进化历史的旧竞争者对其的竞争抑制效应更强烈。这说明了，拥有不同共进化历史的竞争者对粗毛牛膝菊在氮沉降背景下的入侵和扩散具有不同的影响效应。.结果说明了，粗毛牛膝菊的中心和边缘种群之间存在显著的形态和遗传分化，该种在扩散的过程中发生了快速进化；其中心种群具有比边缘种群更高的竞争和扩散优势；在氮沉降背景下，中心种群将维持比边缘种群更高的入侵潜力，旧竞争者将对入侵种产生更高的竞争抑制效应，而新竞争者的抑制效应较低。结果暗示了入侵种粗毛牛膝菊未来的入侵进程将受到种群分化、不同共进化历史的本地种的竞争效应，以及氮沉降增加的共同作用。本研究是对物种共进化、种间相互作用机制的创新与深化发展，将为准确预测氮沉降增加背景下粗毛牛膝菊的入侵动态和科学预防该种入侵提供坚实的科学依据。